This invention relates to continuously variable traction drive transmissions and more particularly, it concerns improvements in torque transmitting bodies for such transmissions as well as in a method and structure for forcing complementary rolling surfaces incorporated in such transmissions into frictional torque transmitting engagement with each other.
In U.S. Pat. Nos. 4,112,779, No. 4,112,780 and No. 4,152,946 several continuously variable transmission embodiments are disclosed in which three frame supported working bodies operate to transmit a mechanical power input to a rotatable output at infinitely or continuously variable speed ratios within the design range of the particular transmission embodiment. In the transmissions of this general class, two of the working bodies are in frictional rolling contact with each other at two points of contact as a result of one of the two bodies being of a biconical configuration to define oppositely convergent rolling surfaces of revolution about one axis and the other of the two bodies taking the form of a rotatably coupled pair of rings defining complementary rolling surfaces about another axis inclined with respect to and intersecting the one axis. The rings are adjustable in a manner to vary the radius ratio of the contacting rolling surfaces and thus attain the continuously variable speed ratio for which the transmission is primarily intended.
Because the structural configuration and torque transmitting functions of the three working bodies are interchangeable in substantial measure as will be appreciated from the several embodiments disclosed in the aforementioned prior patents, it is helpful to use arbitrary terms which identify the respective bodies in the context of the two transmission axes. Hence, where used hereinafter, the term "alpha body" identifies one of the three working bodies which is concentric with the primary or first transmission axis; the term "beta body" identifies another of the three working bodies which is supported by or from the alpha body to be concentric with a second transmission axis which is inclined with respect to and intersects the first or primary axis; and the term "omega body" identifies the last of the three working bodies which is concentric with the first axis and which is rotatable or not rotatable independently in relation to the alpha body. Although these terms are arbitrary as mentioned, they are selected to facilitate a relation of working components to speed ratio equations given in the prior patents and in other publications and which have consistently used the Greek letters .alpha., .beta. , and .omega. to designate the rotational speeds of the three bodies, respectively.
Heretofore, a preferred way of retaining the engaged rolling surfaces in contact under normal force loads adequate to achieve torque transmission by friction has been to provide the biconical body as an assembly of two conical members on a common shaft in concentric fashion and to connect the shaft with a cam system operable to forcibly separate the cone members along the axis of the shaft in response to a torque differential between the shaft and the cone members. This construction has been used in previously disclosed embodiments both where the biconical body is the nutatable beta body and where it is a rotatable omega body. By coupling the shaft either directly or indirectly to the transmission output load, the force by which the cone members would be urged against the ring-like members could be made proportional to output load. A major difficulty with this approach to normal force development is that the nature and magnitude of the loads imposed on the assembly of cone members and shaft tend to deflect the shaft relative to the cone members causing the cone members to bind or otherwise develop an unwanted path of torque transmission between the shaft and the cone members. The effectiveness of the cam or ramp system operative between the shaft and the cone members is, therefore, reduced with the result that the normal forces developed at the points of frictional contact are lower than that required to handle the output load of the transmission. This situation, in turn, can result in slippage of the frictionally engaged surfaces, unequal loading at the two points of contact and other factors which reduce efficiency of power transmission and/or cause damage to transmission components. While various solutions to this problem have been proposed and demonstrated to be effective, in retrospect, such prior solutions have entailed structural complexity and compromise rather than elimination of potential sources of power transmitting efficiency losses and mechanical failure.